In its capacity as the simplest of atoms, atomic hydrogen plays a central role in physics, serving as an ultimate reference point, a basic model of a bound quantum system, and a source of closed-form analytical solutions for quantum theories [1]}, [2]}. The significance of the H atom for the development of quantum concepts is well-documented in the canonical accounts of the early era of quantum mechanics [2]}, [4]}, [5]}. In a more recent history, atomic hydrogen has continued to stay one of the most extensively studied objects of fundamental [6]}, [7]}, [8]} and applied [9]}, [10]} spectroscopy, as well as attosecond physics [11]}, [12]}, [13]}, serving as the basis for understanding the structure of matter and a highly sensitive probe for experimental tests of the quantum theory [14]}, [15]}.
